90 Beekeeping 



temperature is about 60° F., the bees do not cluster com- 

 pactly and do not fly from the hive, even on bright days, 

 but remain inactive on the combs. In this condition they 

 are less active than at any other time in the cycle of the 

 colony and approach most nearly to a condition of hiberna- 

 tion. During the warmer days there is no need of a tight 

 cluster, for the function of the cluster is the conservation of 

 the heat generated within. When the temperature is suffi- 

 ciently high the bees generate no heat but, whenever the 

 temperature of the air immediately surrounding the bees 

 drops below 57° F. (the lowest temperature which normal 

 bees ever experience in the hive), they form a definite cluster. 

 As the outside temperature continues to fall, the cluster 

 becomes more and more compact and the temperature of 

 the inside of the cluster increases rapidly. After the genera- 

 tion of heat is begun, the temperature within the cluster 

 soon reaches a point higher than that reached before heat 

 generation was necessary. Within certain limits, the tem- 

 perature of the cluster increases as the outside temperature 

 drops and, as the outer temperature again rises, heat gen- 

 eration is reduced or discontinued while the temperature of 

 the cluster drifts to meet the rising outside temperature. 

 Heat generation is renewed if the outer temperature again 

 drops, even though the temperature of the cluster and that 

 of the outer air have not yet been equalized. This pro- 

 duces a peculiar inverse relationship between the outer 

 and cluster temperatures. It is of particular practical 

 importance that, within certain definite limits, the bees are 

 not compelled to produce heat. 



Conservation of heat. 



The cluster consists of a hollow sphere of bees several 

 layers thick, those between the combs with their thoraces 

 in contact and abdomens extending outward. The cells 

 within the cluster are also filled with bees. The hair on 

 the thorax assists in making this living shell an excellent 

 non-conductor of heat, so effective in fact that a point in- 



